A favour - reference needed for a claim made in The End of Faith

Hi, I’m currently in an argument about whether the 9/11 attacks were religiously or politically motivated. My copy is on loan but I believe this phrase was originally from the book:

And yet, while the religious divisions in our world are self-evident, many people still imagine that religious conflict is always caused by a lack of education, by poverty, or by politics. Yet the September 11th hijackers were college-educated, middle-class, and had no discernible experience of political oppression. They did, however, spend a remarkable amount of time at their local mosques talking about the depravity of infidels and about the pleasures that await martyrs in Paradise.

Is this referenced, and if so, can someone please provide the reference? Apparently the authority of Sam alone isn’t enough! Crazy!